Also known as: Cストリング, C字裤, Iバック
A strapless Thong shaped like a C, playing on the word G-String. The c-string uses a flexible frame to hold itself to the body without straps to avoid Tanlines.
Generally, this would preclude a Cameltoe but rules of artistic license apply. If a potential c-string doesn't continue all the way up into a back thong "strap" or if it clings too tightly to the body, it might be a Maebari instead.